During the calling of 911 to initiate an emergency call to a Public Service Access Point or PSAP, it is only with difficulty that the telephone number of phone which is making the emergency call can be ascertained. Although the ANI or Automatic Number Identification can, in some instances, be obtained through signalling from the particular cellular phone involved, only massive changes to carrier cell sites and infrastructure will provide a universal solution to a problem plaquing the public safety community. The requirement for the phone number of the phone placing the call is now mandatory in order to enable emergency personnel to call back a stricken individual in the case of a dropped call which happens frequently. Without the ability to speak to the caller, his condition or problem cannot be ascertained.
Note that when a cellular phone is turned on, every six to eight seconds it outputs its ESN or electronic serial number. For each carrier, when a cellular phone is activated, the carrier assigns a Mobile Indentification Number or MIN. When the SEND key is depressed, the phone sends out both the ESN and the MIN. Thereafter, the carrier's switch verifies that the MIN is associated with the ESN for billing purposes.
While the MIN is available at the switch at the time the call is placed, because of the multiplicity of systems, ascertaining the MIN and transmitting it to the PSAP is all but impossible without massive infrastructure changes.
Note that at the present time, there are no standards for MIN reporting, as the system has been developed on an adhoc basis. The Cellular Telecommunications Industry Association estimates eight years to have standards and infrastructure in place in order to meet the requirements to report the mobile caller's telephone number to the appropriate PSAP.
Representative systems for determining the MIN are as follows: The most common arrangement now in place for reporting any telephone number to the appropriate PSAP, although not the actual phone number of the caller, according to the Jun. 1996 15th Annual Conference of the National Emergency Number Association is that upon receipt of a telephone call from a cellular phone, the cell site assigns the call a ten digit telephone number from a list of phone numbers provided by the state. The purpose of this telephone number is to identify the cell site receiving the call, not the caller's telephone number. Then, the cell site transmits a "911 send" signal to the Mobile Telephone Switch Office or MTSO from the cell site, with the 10 digit telephone number or TN then transmitted to the Local Exchange Carrier or LEC Central Office or Access Tandem. This office then routes the call to the appropriate E-911 Tandum Switch that routes the call to the nearest PSAP under control of a Data Management System. Simultaneously, the LEC Central Office separately transmits the 10 digit Admin TN to the PSAP. Here, the 10 digit telephone number is merely used to identify the receiving cell site to obtain the general area from which the emergency call was initiated. While some PSAPS attempt to use this 10 digit Admin TN to try to contact the caller, this is only done with difficulty, if at all.
A second system for reporting the telephone number of the cell site, but not the caller's telephone number relies on a Psuedo-ANI or Psuedo Automatic Number Identifier that is not assigned by the state, but rather by the carrier and is generated at the receiving cell site. This number is provided to the MTSO which, in turn, is routed as the ANI to the 911-Tandem. The Psuedo-ANI is processed by the E-911 Tandem to transmit to the PSAP the pseudo telephone number, carrier name, cell cite address, cell site latitude and longitude, roam access number, serving radius and sector bearing. Again, the telephone number of the caller is not reported, with the reported phone number merely identifying the location of the receiving cell site.
A third system provides the real ANI, i.e. the real telephone number of the caller, with the real ANI coming from the cellular phone. Note, the psuedo ANI is also generated at the cell site at this time. The "911-send" is transmitted to the LEC Central Office, with the LEC Central Office being provided with the psuedo-ANI, the real ANI, and the Feature Group D or SS7 trunk. As a result, the LEC Central Office provides the PSAP with the Real ANI, the Pseudo ANI and a psuedo automatic location indication or ALI derived from knowing which cell site received the call. While the real ANI permits a call back to the caller by the PSAP, having the phone digitally provide its telephone number, suffers not only from infrastructure costs, but also from problems surrounding the fact that there is no commonly agreed-upon format. Thus, the system is not universal until such time as all carriers and all phone manufacturers agree on a format such as CDPD, CDMA, TDMA, or FDMA, e.g. respectively cellular digital packet data, code division multiplexing, time division multiplexing, or frequency division multiplexing.
A fourth system adds actual location information calculated from triangulation from different cell sites, while providing the PSAP with the real ANI, the psuedo ANI, the pseudo ALI, and both the latitude and longitude and speed/direction of the cellular phone. Also provided is the subscriber name and subscriber home address.
A fifth system provides all of the information of the fourth system described above, but derives latitude and longitude from GPS satellites, with the latitude and longitude being digitally transmitted to the cell site, which is, in turn, relayed to the PSAP.
It will be appreciated that all of the above approaches to providing the PSAP with the telephone number of the caller is infrastructure intense, requiring major changes to switches at the cell sites, major additions to the MTSO and LEC Central Office and major additions to databases. Moreover, providing either the 10 digit TN or pseudo ANI's is, at best, confusing and, at worst, can result in a wrong telephone number being dialed by the PSAP if the cellular phone moves to a different cell site.
The result is massive infrastructure changes and years to implement, to say nothing of the compatibility of networks from state to state, or even between different carriers in the same geographic area.
Thus, since there are numerous different ways of obtaining the caller's telephone number, all involving changes to cell site switches, complicated computer interfaces, and billing related issues, there is no universal way of ascertaining the number of the telephone making the emergency call, especially at the PSAP where it is required.
As a result, frustration abounds when a cellular phone call to a PSAP is dropped since there is no way for the PSAP to reestablish the communication link between the PSAP and the stricken individual. Moreover, the identity of the individual owning the phone is not known since the telephone number of the telephone cannot be ascertained at the PSAP.
It is therefore paramount to be able to provide a simplified universal system for providing the PSAP with the telephone number of the calling party so that both interrupted emergency communications can be reestablished and the identity of the owner of the particular phone making the cellular phone call can be reported to the PSAP.